If you're looking to monitor traffic to localhost, bind the the `lo0` interface. For example, when I'm monitoring traffic to a local Rails app in development, I

If you're looking to monitor traffic to localhost, bind the the `lo0` interface. For example, when I'm monitoring traffic to a local Rails app in development, I'll do something along the lines of: sudo tcpflow -c -n lo0 src or dst post 3000 and it'll pick up the traffic. (Thanks for the tips on alternative ways of monitoring TCP traffic flows, folks!)